Men and women are being paid £2,000 (€2,900) a time to go through with sham marriages to foreign nationals in the North, it was revealed today.

At least 12 agreed to sign the register as part of a human trafficking operation involving Nigerians seeking UK citizenship.

It is understood they paid the men running the racket as much as five times the wedding fee to gain entry.

Police believe that a number of people from West Africa approached men and women as far back at 2002 in the Derry area.

Detectives today confirmed a major inquiry was underway.

A Northern Ireland Affairs Committee report last month revealed the growing trade in human trafficking, some of it linked to paramilitaries, but it is not thought they are connected to the Derry inquiry.

Immigration Service is to set up an office in Belfast after concerns were raised about the problem.

In May 2006 Women's Aid gave evidence to a Westminster Committee highlighting the trafficking problem and called for action.

Paramilitaries are involved in human trafficking but are not involved in this investigation.

East Derry Assemblyman John Dallat said he was alarmed. "The people involved in this need to be caught, it is something which we don't want to see happening here," he said.

"It is becoming more and more difficult for legitimate people to gain entry and it is because of operations like this that it is becoming harder for people. I would be concerned about this kind of activity and would like to see it stop."

Two Nigerian men were charged in Derry at the end of May with facilitating unlawful entry of immigrants into the UK. A third was released without charge.